This invention relates to a powder molding press and controlling the to action of a lower ram in accordance with the movement of an upper ram.
FIG. 7 is a working characteristic diagram showing movements of a punch and die of a conventional molding press. In order from the top, stroke diagrams of the upper and lower rams, a pressurizing diagram of the upper punch, a velocity diagram of dies, and a working force diagram acting on the dies are shown. The movements of the upper punch and die in one working cycle are shown in FIG. 7. In the present invention, on the other hand, a motor driving the dies keeps constant torque regardless of its speed, accordingly, in selecting the motor capacity, it is necessary to satisfy the maximum speed for driving rams, and also to satisfy the maximum output force. With respect to the general motor characteristic on the relation between the force and speed affecting the dies, the speed is fast and the pressing force is small at the compression starting point, and in accordance with the progress of the compression stroke, the pressing force gradually grows larger and the compressive speed conversely becomes smaller.
With smaller force, the speed becomes faster, and with a larger force the speed tends to be slower, so in order to obtain both a larger force and higher speed, it is necessary to increase motor capacity, which entails higher production and operating costs.
The present invention was developed in consideration of the above-mentioned problems, and its object is to provide a powder molding press able to obtain sufficient compressive force and working speed even if provided with small motor capacity, by installing a pair of non-circular gears able to mechanically change the speed ratio between the motor and the lower ram for pressing dies.